Cellulose esters and products thereof



A accelerated -by the presence during saponifica- Patented Sept. 7, 1937UNITED STATES 2,091,968 CELLULOSE EgTERS AND PRODUCTS HEREOF HenryDreyfus, London, England No Drawing. Application January 4, 19-35,Serial No. 326. Renewed April 16, 1937.

In Great Britain January 13, 1934 16 Claims.

This invention relates to the treatment of cellulose acetate and otherorganic esters of cellulose and particularly to a process for reducingthe acidyl content of such esters. The in- -vention is speciallyapplicable to the saponification of filaments, threads, yarns, ribbonsand the like made of or containing such esters.

It is known that in general where mineral alkalies are employed tosaponify materials of the type referred to above, the saponificationtends to be superficial, so that while the surface of the material isintensively saponified, a core of substantially unsaponified esterremains, Moreover, saponification by such agents when apterial, whilethe serimetric properties of the material may actually be improved bythe process. I have now found that saponification by means of suchnon-metallic bases may be considerably tion of alkali metal salts ofalkaline reaction which are themselves saponifying agents without thepresence of the salt leading to superficial saponification. The processin fact provides a rapid method of obtaining threads and like materialsof good tenacity, extensibility and elasticity which are saponified to aconsiderable depth below the surface or even throughout the whole crosssection.

Alkaline salts particularly suitable for use in the process of theinvention are found among the alkali metal salts of very weak acids, forexample carbonic acid and hydrosulphurous acid. The acid may be organicor inorganic. It is of great advantage to saponify filaments, threadsand like materials non-superficially, i. e. so that there is no sharpand substantial change in the degree of saponification from the surfaceof the material to a point at some depth below the surface. With thisend in view it is in general of advantage to employ the salt in as smalla concentration as is consistent with obtaining the desired speed ofsaponification. The proportion in which a particular salt should beemployed depends largely upon the nature of the salt, for example thestrength of the acid from whichit is formed. With salts such as thesulphides and carbonates of sodium and potassium, for example, verysmall quantities, for instance 1-2 or 3% or even less, enablenon-superficial saponification to be eifected very rapidly. Other salts,for example the borates and phenates of sodium and potassium, requiresomewhat higher concentrations, for instance 4-5 or 6%, to bring about asimilar acceleration of the saponifying process and the results aresomewhat less satisfactory. The alkali metal salt is preferablyintroduced into the sapom'fying bath itself, although other suitablemethods of application are not excluded.

The organic ester of cellulose treated may be of normal or lowviscosity, for example in the case of cellulose acetate the viscositymay be of the order of 30 to 50, 100, 200 or even higher, these figuresbeing obtained by comparison of a 6% solution of the ester in acetone at25 C. with .glycerine at the same temperature taken as a standard of100. Such esters of high viscosity may readily be made by methods inwhich degradation of the cellulose. molecule is substan tially avoidedduring acidylation. On the other hand, the viscosity of the celluloseacetate employed may be of the order of 10-20 or even lower, or between20 and 30, measured on the scale referred to above.

The invention is of particular importance in connection with thesaponification of filaments, threads, ribbons, fabrics and likematerials having a basis of cellulose acetate and will be described withspecial reference to the treatment of such materials.

The materials treated may be made by any suitable dry or wet spinningmethod. Where high tenacity is required in the final products it is ofparticular advantage to produce the filaments and the like by wetspinning methods in the course of which they are stretched to aconsiderable extent, or to soften and stretch the materials after theirproduction whether by a wet or a dry spinning process. By applying theprocess of the invention to materials which have been stretchedconsiderably, for example to 200% of their original length or even more,materials of particularly valuable serimetric properties are obtainable.

Particularly good results are obtained by the use of saponifying bathscontaining methylamine and the alkaline salt. Other strong aliphaticorganic bases, for example ethylamine, propylamine, amylamine andtriethylamine, may also be employed. Again, somewhat weaker bases of thesame series, for example trimethylamine and allylamine, may be iised.Further, considerably stronger bases of the same series may be employed,even very strong bases such as tetra-. methyl ammonium hydroxide,provided care be taken to avoid damaging the. materials. Aminescontaining more than one amino group, and particularly aliphaticdiamines of relatively low molecular weight, for example ethylenediamine,

symmetrical. dimethyl ethylene diamine, monomethyl ethylene diamine andpropylene diamine may also be used. Preferably at least one of the aminogroups of such amines should be unsubstituted or monosubstituted. Aminescontaining more than two amino groups may also be employed, for example1.2.3-triamino propane. The efiect of one or more hydroxy groups in theamine appears to be to favour .the penetration of the materials by thesaponifying agent, and with this object in view substances of the typeof wy-diamino-fi-hydroxy propane may be used with advantage. The use ofbases of the heterocyclic series, for example piperidine is notexcluded.

As indicated above saponification is preferably efiected by subjectingthe materials to an aqueous bath containing methylamine or a like actingbase and small quantities of the alkaline salt in solution. Generallyspeaking concentrations of non-metallic, base of about l0-30%, forinstance 1525% will be found suitable. Although it may be of advantagein some cases to work at atmospheric temperature, or even at a lowertemperature, somewhat higher temperatures are in general to bepreferred, for example from 25 or 30 C. to 40, 50 or even 60 C. orhigher, depending on the boiling point of the solution. Witha View topreventing excessive evaporation of the base it is of advantage,particularly when working at relatively high temperatures, to cover thesurface of the saponifying bath with a layer of an oil, wax or likesubstance which is immiscible with the bath. The time during which thematerials are in contact with the bath will naturally vary according tothe amount of saponification to be effected, the nature of the bath andthe temperature of treatment. Thus the time of treatment may vary fromless than one minute, for instance 15-30 or seconds to two or threeminutes, or even longer where a relatively slow acting base is employed.The material should not be allowed to remain in the bath aftersaponification is complete.

saponification may be efiected in the presence of other substancescapable of accelerating the reaction in addition to the alkaline salt.The use of certain metals in accelerating saponification by methylamineand like acting bases is described in the co-pending U. S. applicationsS. Nos.,756,284 and 756,285 filed December 6, 1934. Such metals may beintroduced in suitable form to the saponifying bath or may be applied tothe materials prior to the saponification, or may even be introducedinto the spinning solutions from which the materials are made. By way ofexample, copper oxide may be introduced into the saponifying bath inquantity suiiicient to produce a concentration of 0.010.5%. When suchmetals are employed in the saponifying bath it will in general benecessary to remove them from the materials after saponification. In thecase of copper removal may readily be efi'ected by treating thematerials with a dilute acid, for

example 20% acetic acid or 2% sulphuric acid. Due regard should, ofcourse, be had to the possibility of reaction between the alkaline saltand the metal.

The saponifying medium may also contain swelling agents, solvents orlatent solvents for the cellulose ester, for example cyclohexanol,methyl cyclohexanol, glycerol, ethylene glycol and its monomethyl anddimethyl ethers, diacetone alcohol, benzyl alcohol, acetone, dioxane ormethylene ethylene ether.

When the materials are treated in. the form of filaments, threads, yarnsand the like; it is of advantage to effect saponification in warpformation, i. e., by drawing a large number of ends through the bath insubstantially parallel relationship-one to another and in the sameplane. Thus,v yarn may be drawn from a creel by means of rollers or likedevices extending across the entire assembly of ends or so-called warpand immersed or partially immersed in a bath containing the saponifyingagent, through a reed into the bath, and after passing through the baththe materials may be drawn by a second roller, pair of rolls or thelike, situated outside the bath, through a reed and out of the bath,whence they are forwarded to suitable collecting means or to means forefiecting any subsequent treatment to be applied. Preferably the materials are washed and dried before being wound.

The saponifying agent may be applied by other means. Thus, for example,the materials in hank form may be suspended from rods which are causedto traverse the length of the bath, and at the same time to rotate so asto expose each portion of the yarn to the same depth in the bath for thesame period. Again, the materials may be treated in the formof bobbins,cheeses or other packages. Any suitable means may in fact be adoptedinapplying the saponifying agent to the materials. Materials in yarn orlike form may be treated continuously with their production and/or witha stretching step. Again, in the case of such materials stretching maybe efiected during saponification or, provided sa ponification has notbeen carried too far, after saponification. In general it is necessaryto soften the materials to enable them to be stretched to the desiredextent, and in choosing a suitable. softening agent due regard should behad to the extent to which the materials have been saponified.

As indicated above, the materials may be saponifiecl in fabric form.This may conveniently be effected by passing the fabric continuouslythrough a bath containing the saponifying agent, for example in anapparatus of the type of the winch dyeing machine.

The materials prior to saponification may be subjected to a treatmentadapted to facilitate penetration of the saponifying agent. This maycomprise the application of water to the materials, or they may betreated with aqueous wetting agents, for example soaps.

The degree of saponification eflfected maybe sufficient to reduce theoriginal acidyl content of the 'ester by 8%, 10% or even less, but ispreferably somewhat higher, for example suficient to remove 20-25 or 30%of the acidyl content. Considerably higher degrees of saponification maybe efiected, for instance so as to remove 35 or 40 to or of the acidylcontent ormore, even up to complete saponification, according to theparticular purpose in vie The saponification may be suflicient to rendercellulose acetate insoluble in substantially anhydrous acetone butsoluble in acetone containing a considerable percentage, for example25-30% of water. Or saponification may render the material insoluble insuch mixtures as well as in anhydrous acetone. The saponification mayraise the safe ironing point considerably. The material may gain anaffinity for cotton dyes and may or may not retain its aflinity forcellulose ester dyes. Materials saponified according to the inventionmay have, in addition to the valuable properties referred to above, ahigh tenacity, good extensibility and elasticity. Materials ofparticular value in the manufacture of high twist yarns may be made bythe process of the invention. Thus, high twist yarns partiallysaponified according to the invention have been found specially usefulas weft in the manufacture of crepe fabrics. Again, by the process ofthe invention it is possible to obtain completely saponified materialsof excellent tensile properties.

The following examples illustrate the invention:

Example 1 Cellulose acetate yarn is led continuously in warp formationfrom a creel through a saponifying bath containing a 15-30% aqueoussolution of mono-methylamine in which is dissolved a small quantity ofsodium carbonate. is maintained at 50-60" C. The speed of travel of thematerials is arranged so that the desired degree of saponification isobtained by the time the materials leave the bath. The saponifiedmaterials are led continuously from the saponifying bath through awashing bath wherein any constituents carried over from the saponifyingbath are removed and are dried by passage over steam, heated rolls andcollected by suitable means.

Example 2 The process is carried out as described in Example 1, exceptthat instead of sodium carbonate, sodium sulphide is employed and thematerials are collected wet in-a centrifugal spinning box. As in thepreceding example the materials are 35 freed from contamination withconstituents of salt of an alkaline reaction the saponifying bath beforebeing dried.

What I claim and desire to secure by Letters Patent is:--

1. Process for reducing the acidyl content of an organic ester ofcellulose, which comprises saponifying the ester by means of anitrogenous organic base in the presence of an alkali metal which isitself a saponifying agent for the cellulose ester.

2. Process for reducing the acidyl content of an organic ester ofcellulose, which comprises saponifying the ester by means ofmono-methylamine in the presence of an alkali metal salt of an alkalinereaction which is itself a saponifying agent for the cellulose ester.

3. Process for the saponification of filaments, threads, ribbons andlike materials having a basis of organic ester of cellulose, whichcomprises treating the materials with a nitrogenous non-aromatic organicbase in the presence of an alkali metal salt of an alkaline reactionwhich is itself a saponifying agent for the cellulose ester.

4. Process for the treatment of filaments, threads, ribbons and likematerials having a basis of organic ester of cellulose, which comprisessubjecting the materials to substantially complete saponificationbymeans of a nitrogenous nonaromatic organic base in the presence of analkali metal salt of an alkaline reaction which is itself a saponifyingagent-for the cellulose ester.

5. Process for the saponification of filaments, threads, ribbons andlike materials having a basis of organic ester of cellulose, whichcomprises treating the materials with a lower aliphatic amine in thepresence of an alkali metal salt of an alkaline reaction which is itselfa saponifying agent for the cellulose ester.

The bath 1 6. Process for the saponification of filaments, threads,ribbons and like materials having a basis of organic ester of cellulose,which comprises treating the materials with ethylene diamine in thepresence of an alkali metal salt of an alkaline reaction which is itselfa saponifying agent for the cellulose ester.

'7. Process for the saponification of filaments, threads, ribbons andlike materials having a basis of cellulose acetate, which comprisestreating the materials with mono-methylamine in the presence of analkali metal salt of an alkaline reaction which is itself a saponifyingagent for cellulose acetate.

'8. Process for reducing the acidyl content of an organic ester ofcellulose, which comprises saponifying the ester by means of anitrogenous nonaromatic organic base in the presence of an alkali metalcarbonate.

9. Process for reducing the acidyl content of an organic ester ofcellulose, which comprises saponifying the ester by means of anitrogenous nonaromatic organic base in the presence of an alkali metalsulphide.

10. Process for the saponification of filaments,

threads, ribbons and like materials having a basis of cellulose acetate,which comprises treating the materials with a 1530% aqueous solution ofmono-methylamine containing an alkali metal carbonate.

11. Process for the saponification of filaments, threads, ribbons andlike materials having a basis of cellulose acetate, which comprisestreating the materials with a 15-30% aqueous solution ofmono-methylamine containing an alkali metal sulphide.

12. Process for reducing the acidyl content of an organic ester ofcellulose, which comprises saponifying the ester by means of anitrogenous non-aromatic organic base in the presence of an alkali metalsalt of alkaline reaction which is itself a saponifying agent for theester.

13. Process for reducing the acidyl content of an organic ester ofcellulose, which comprises saponifying the ester by means of anitrogenous non-aromatic organic base in the presence of a smallquantity of copper and an alkali metal salt of an alkaline reactionwhich is itself a saponifying agent for the cellulose ester.

14. Process for the treatment of filaments,

threads, ribbons and like materials having a basis of cellulose acetate,which comprises saponifying the materials to remove from to 30% of theoriginal acetyl content by means of a nitrogenous non-aromatic organicbase in the presence of an alkali metal salt of an alkaline reactionwhich is itself a saponifying agent for cellulose acetate.

15. Process for the saponification of filaments, threads, ribbons andlike materials having a basis of organic ester of cellulose, whichcomprises treating the materials with a nitrogenous organic basecontaining pentavalent nitrogen in the presence of an alkali metal saltof alkaline reaction which is itself a saponifying agent for the ester.

16. Process for the sapom'fication of filaments, threads, ribbons andlike material having a basis of cellulose acetate, which comprisestreating the materials with tetramethyl ammonium hydroxide in thepresence of an alkali metal salt of alkaline reaction which is itself asaponifying agent for the cellulose acetate.

HENRY DREYFUS.

